The present invention is drawn to a refrigeration cycle and, more particularly, to a Joule-Thomson refrigeration cycle which employs an electrochemical compressor having a solid polymer electrolyte.
Joule-Thomson refrigeration cycles are well known in the art and have been the subject of much study in the last few years. The basic principle of the Joule-Thomson refrigeration cycle resides in pumping a gaseous working fluid (e.g., hydrogen) at high pressure through a series of heat exchangers and a Joule-Thomson (J-T) valve. Expansion of the gas at the J-T valve results in a net cooling effect, which lowers the fluid's temperature to levels near or at the liquefaction point.
It has been proposed in the prior art to use an electrochemical compressor to drive a Joule-Thomson refrigeration cycle. See, for example, U.S. Pat. No. 4,593,534 to Bloomfield. Ideally, this type of compressor is preferred since it has no moving parts. The system is therefore vibration free and has the potential for long life and high reliablity.
A typical electrochemical compressor comprises a first electrode, wherein the working fluid having an electrochemically active component, generally hydrogen, is oxidized; a second electrode, wherein the electrochemically active component is reduced; and an electrolyte which serves to conduct the ionic species. The electrolyte is generally a solid ion exchange membrane such as NAFION, a solid polymer electrolyte manufactured by E. I. Du Pont de Nemours & Co., Inc. of Wilmington, DE.
Operation of the electrochemical compressor is as follows. Low-pressure hydrogen at the compressor inlet is ionized at the first electrode by removal of the electrons. The hydrogen ions, protons, are then transported via a voltage potential across the electrolyte membrane. At the second electrode, the protons are recombined with their electrons to form hydrogen. Platinum, provided as a catalyst at each electrode, facilitates the reduction and oxidation reactions. Hydrogen is transported through the membrane in direct proportion to the electrical current.
When operating the electrochemical compressor, the solid polymer membrane must be hydrated. Otherwise, the cell performance will seriously degrade with time.
Applicant has recognized a dehydration problem. Moisture is, unfortunately, continuously removed from the membrane as the gas passes through it. Since contaminates, such as water, cannot be tolerated in a Joule-Thomsom refrigeration cycle, the gas is then passed through a sorbent bed. There, the carried moisture is condensed and frozen out, or absorbed.
Applicant has determined that the cell's efficiency and useful life will be prolonged if the membrane is continuously wetted, or hydrated. It would therefore be highly desirable to provide a Joule-Thomson refrigeration cycle, employing an electrochemical compressor, which allows for its solid polymer electrolyte membrane to be continuously hydrated by water carried in the working fluid.
Accordingly, it is the principal object of the present invention to provide an improved Joule-Thomson refrigeration cycle in which this constant wetting of the polymer member is achieved by a condensable component in the working fluid.
It is a particular object to provide a refrigeration cycle, which employs regenerable sorbent means upstream and downstream of the electrochemical compressor for removing water from the high-pressure working fluid and replacing water into a low-pressure working fluid.
It is another object to provide a refrigeration cycle, commenstrate with the above-listed objects, wherein the electrochemical compressor is driven by a reverse-polarity power source so as to selectively reverse gas flow through the compressor in the refrigeration cycle.
The above and other objects and advantages of this invention will become more readily apparent when the following description is read in conjunction with the accompanying drawing.